1. Field of the Invention
This invention relates broadly to a process for dyeing fibers. More particularly, this invention relates to a continuous process for dyeing raw cotton fibers.
2. State of the Art
A bale of cotton generally comprises non-cohesive clumps of raw cotton fibers in varying sizes and thicknesses. Due to the difficulty in working with the non-cohesive clumps, raw cotton fibers are dyed in a batch process. In the batch process, raw cotton fibers are compressed into a perforated cylinder wrapped in a wire basket having a handling hook at the top. A crane lifts the wire basket by the hook and lowers the cotton batch into a pressured dye kettle where the cotton is immersed in a dye solution. The cotton, which is now in the pressurized kettle, is dyed under pressure for a period of time, e.g., four hours, allowing the dye to be fully absorbed into the cotton. After dyeing, the cotton batch is rinsed to take out excess dye. Afterward, a crane is operated to lift and move the cotton in the basket to a centrifical extractor which extracts or otherwise removes excess water from the cotton. The dyed cotton fiber, also referred to as stock dyed cotton, is then dried with heat and air before entering into the spinning process.
Because raw cotton fibers are dyed in a batch process, the color of the dyed cotton will undesirably vary from batch to batch even where the dye solution provided to each batch is closely controlled. A continuous process with an "endless" dye lot can provide a better consistency of color. However, while it has been long known in the art that a continuous dyeing process would be desirable, to date, no commercially feasible solutions have been provided for such a continuous process.
It is known to dye fabrics (as opposed to fibers) in a continuous dyeing process rather than in a batch process. In the continuous fabric dyeing process, a roll of uniformly flat, continuous, knit or woven fabric is held taught and fed between dye pressure rollers which apply dye to the fabric. However, because raw cotton is neither flat, uniform in thickness, or continuous, it is not possible to adopt the continuous method of dyeing fabrics for use in dyeing raw cotton fibers.